The present invention relates generally to nipples utilized in subterranean wells and, in a preferred embodiment thereof, more particularly provides an improved full bore nipple and a lock mandrel for use therewith.
In a subterranean well, one or more nipples are typically installed as part of a tubing string positioned within the well. Such nipples may serve many purposes. For example, a nipple may serve as a positive positioning device, by providing an internal shoulder or other profile for landing equipment within the tubing string. As another example, a nipple may serve as a sealing device, by providing an internal seal surface which may be sealingly engaged by equipment disposed therein.
Where circumferential seals, such as packing or orings, are carried externally on equipment disposed within the nipple, it is common practice for such seals to have a smaller diameter than the tubing's internal drift diameter. In this way, the seals may easily pass axially through the tubing string to the nipple. Accordingly, internal seal surfaces of nipples typically have a smaller diameter than the tubing's drift diameter, so that the seal surfaces may sealingly engage the seals.
Unfortunately, a nipple seal surface which is smaller than the tubing drift diameter presents a restriction in the tubing string. Such restriction inhibits fluid flow through the tubing string, is quickly eroded by such fluid flow, restricts the diameter of equipment which may be passed axially therethrough, and otherwise inhibits operations in the well. For these reasons, it is generally desirable for all portions of the tubing string to have a minimum internal diameter which is at least as large as the tubing drift diameter. Those portions of a tubing string meeting this requirement are said to be "full bore".
Recently, full bore nipples have become available and are well known to those skilled in the art. For example, U.S. Pat. Nos. 5,348,087 and 5,390,735, each of which is assigned to the assignee of the present invention, disclose full bore nipples and lock mandrels therefor. The disclosures of these patents are hereby incorporated herein by this reference. In basic terms, such full bore nipples have a seal diameter at least as large as the tubing drift diameter, and the lock mandrels therefor have a seal which is radially outwardly extendable, so that the seal may pass through the tubing string when the seal is inwardly retracted, and the seal may sealingly engage the seal surface of the nipple when the seal is outwardly extended.
However, with the seal surface of a full bore nipple being generally aligned with the tubing drift diameter, several problems remain associated therewith. For example, the seal surface is still directly exposed to fluid flow through the tubing string. Where the fluid is abrasive, or carries abrasive particles therewith, the seal surface may become eroded, and weight loss corrosion may also result from the fluid flow. As another example, the seal surface may be damaged by equipment passing axially therethrough. As yet another example, the seal surface may be damaged by slickline, wireline, coiled tubing, etc., cutting into the seal surface as the slickline, etc., is axially reciprocated within the tubing string.
From the foregoing, it can be seen that it would be quite desirable to provide a full bore nipple which includes a recessed seal surface that is protected from fluid flow and equipment, slicklines, etc., passing through the nipple. Additionally, it would be desirable to provide a lock mandrel for such a full bore nipple, which is capable of locking to the nipple and sealingly engaging therewith. It is accordingly an object of the present invention to provide such a full bore nipple, lock mandrel therefor, and associated methods of configuring a tubing string within a subterranean well. Other objects, features, and benefits of the present invention will become apparent upon consideration of the detailed description hereinbelow.